An important component in any imaging application is the lens design. When space is not an issue, a lens design typically utilizes more than two separate lenses in the lens design. For example, a first lens can be utilized for color separation functions, while a second lens can be utilized for ray bending functions.
Consumers are most familiar with finding lens in cameras and video cameras. In these applications, there is typically no size restriction on the size of the lens assembly. However, there has been recent interest in designing cameras in electronic devices where cameras did not exist previously. These space critical applications have very strict size limitations for the lens assembly. The size requirement is often expressed as a distance between an aperture and a focal plane and is generally known as the “height”. For example, one such application proposes to integrate a camera into a cell phone for video-conferencing capabilities. Such an application requires a height of no more than the average thickness of the cell phone, which as can readily appreciated, is much less than the height of most hand-held camera applications.
Unfortunately, the prior art lens designs have heights of about twice the size requirements of these space critical applications.
When designing a lens system under a strict height requirement, it is generally not possible to use more than a single lens. In a single lens design, there is a need to use a diffractive surface for performing color correction functions. One challenge of using a diffractive surface is to design the surface in such a way as to increase the diffraction efficiency. The diffraction efficiency is related to how well the lens places light on the focal plane at desired locations. For example, a very efficient lens converges the incident light rays at discrete points (known as spots) along the focal plane. As the diffraction efficiency of the lens decreases, the size of the spots increases. As the spot size increase, the resulting image loses clarity and become fuzzier.
Unfortunately, the prior art single lens designs exhibit low diffraction efficiency, thereby leading to a fussy image.
Another challenge in single lens design is that the image exhibits vignetting (or shadowing) of the corners of the image. Accordingly, it is desirable for the single lens design to have a mechanism that reduces the amount of vignetting (or shadowing) of the corners of the image.
Consequently, it is desirable to design a singlet that has excellent resolution over a large field of view and a small height to meet space critical imaging applications.